In recent years, mobile telephones (including so-called “cellular phone” or “smartphone”) that make a connection to a mobile telephone network are provided with a wireless LAN communication unit (Wi-Fi (registered trademark) function conforming to the IEEE 802.11 standards), and such a mobile telephone can be used to connect to the Internet under a wireless LAN environment at home or at an office (hereunder, referred to as “in the home”) and utilize a variety of Internet services such as Web browsing and IP telephone services and the like.
In the home, a cordless telephone set that makes a connection to a landline telephone network is provided, and the cordless telephone set is shared by a plurality of people such as family members, while a mobile telephone is used for personal use. Thus, the cordless telephone set and the mobile telephone are utilized as telephone sets for completely independent uses. In this respect, technology that connects such a cordless telephone set to a mobile telephone is disclosed, for example, in PTLs 1 to 3.
PTL 1 discloses a cordless telephone system that uses PHS (Personal Handy-phone System) technology to enable, by switching a communication mode of a mobile telephone between a public-network mode and a home-network mode, combined use of the mobile telephone as a mobile telephone when outdoors and as a portable unit of a cordless telephone set in the home.
PTL 2 discloses a telephone set system in which a wireless IP telephone (portable unit) is connected to a base unit having a telephone network control circuit (landline telephone network communication unit) and a digital wireless communication unit (wireless LAN communication unit) to thereby utilize the wireless IP telephone as an Internet wireless telephone set.
In addition, PTL 3 describes a multifunction machine that includes an existing cordless telephone transceiver unit and a wireless LAN transceiver unit and in which a cordless telephone and a wireless LAN coexist, and which enables calls without sound interruptions or delays with a cordless telephone set.